I'm fairly sure that people only "knew" what an incorrectly-taken throw was in the same way that they "knew" that a player standing in an offside position was guilty of an offside offence even if they weren't involved in active play.
The laws have never given any more detailed description of the exact mechanics of a throw, than they do now. Here for instance, is the law wording from 1903:
And from 1925:
1932:
1960:
1997:
As
@ChasObserverRefDeveloper alluded to, none of these earlier versions of the law specified a release point (or talked about the trajectory the ball had to take after being released).
So I'm not sure that people could have known with any greater degree of certainty in the past than they do now, what an improperly-taken throw-in was, since the law has never been particularly precise about mechanics, in any of its incarnations.